J/psi production from proton-proton collisions at square root of s=200 GeV

J/psi production has been measured in proton-proton collisions at square root of s=200 GeV over a wide rapidity and transverse momentum range by the PHENIX experiment at the Relativistic Heavy Ion Collider. Distributions of the rapidity and transverse momentum, along with measurements of the mean transverse momentum and total production cross section are presented and compared to available theoretical calculations. The total J/psi cross section is 4.0+/-0.6(stat)+/-0.6(syst)+/-0.4(abs) mu b. The mean transverse momentum is 1.80+/-0.23(stat)+/-0.16(syst) GeV/c.     

Measurement of the inclusive jet cross section in pp[over] collisions at square root [s]=1.96 TeV

We report on a measurement of the inclusive jet cross section in pp[over ] collisions at a center-of-mass energy sqrt[s]=1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0.70 fb;{-1}. The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.     

Correlations between transverse energy production and the Drell-Yan process in heavy ion collisions at high energy

The expression for the Drell-Yan cross section is presented which takes into account the geometry of heavy ion collisions. The Drell-Yan cross section is shown to be proportional to the transverse energy produced within a fixed rapidity interval. A dependence steeper than linear of the cross section for production of dileptons with masses larger than about 2 GeV on the transverse energy in a given rapidity bin would be a clear-cut signal for the formation of the quark-gluon plasma.     

Hadron production ine +e− annihilation and μ-p collisions under the assumption of longitudinal phase space dominance

Rapidity and multiplicity distributions are calculated for the hadrons produced ine ⁺e^? annihilation and deep inelastic muon-proton collisions for c.m. energies of 10 to 40 GeV. The hypothesis of longitudinal phase space dominance leads to a probability distribution which is identical to that of a grand canonical ensemble of non-interacting particles. We successfully describe experimental rapidity distributions, domains of Feynman-x scaling and scaling violations and the rapidity dependence of the mean transverse momentum. Multiplicity distributions are derived to be close to negative binomial distributions even for finite rapidity intervals. The plateau in the rapidity distribution is the origin for the negative binomial distribution in multiplicity. The mean number of hadrons of each species and the mean overall transverse momentum are the main input parameters in our calculation and are taken from experiment.     

Using dileptons to probe the color glass condensate

The rapidity and transverse momentum dependence of the nuclear modification ratio for dilepton production at RHIC and LHC is presented, calculated in the color glass condensate (CGC) framework. The transverse momentum ratio is compared for two distinct dilepton mass values and a suppression of the Cronin peak is verified even for large mass. The nuclear modification ratio suppression in the dilepton rapidity spectra, as obtained experimentally for hadrons at RHIC, is verified for LHC energies at large transverse momentum, although not present at RHIC energies. The ratio between LHC and RHIC nuclear modification ratios is evaluated in the CGC, showing the large saturation effects at LHC compared with the RHIC results. These results consolidate the dilepton as a most suitable observable to investigate the QCD high density approaches.     

Transverse-momentum fluctuations in pi(+)p and K(+)p Collisions at 250 GeV/c

We report results on event-by-event fluctuations of transverse momentum, Phi(p(t)), in pi(+)p and K(+)p collisions at 250 GeV/c. For the first time, their dependence on rapidity region, transverse momentum acceptance, multiplicity, mean transverse momentum per event, and on the correlation between transverse momentum and multiplicity are systematically presented. The results are compared with those from the PYTHIA Monte Carlo generator. The fluctuations under the same acceptance cuts as used in current heavy-ion experiments are also presented.     

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4相似文献   

On the anomalous large transverse energy events observed in proton-lead scattering

It has been shown that a study of correlation between the average rapidity, 〈y〉, and transverse energy,E _T , can be used to distinguish between different origins of large transverse energy events observed inp-Pb scattering in the HELIOS experiment. If the largeE _T events are to be attributed to a nuclear dependence of structure functions then the hard scattering picture implies a positive correlation among the above two quantities, contrary to that seen in experiment.     

Effect of the momentum dependence of nuclear symmetry potential on the transverse and elliptic flows

In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, the effect of the momentum dependence of nuclear symmetry potential on nuclear transverse and elliptic flows in the neutron-rich reaction ¹³²Sn+¹²⁴Sn at a beam energy of 400MeV/nucleon is studied. We find that the momentum dependence of nuclear symmetry potential affects the rapidity distribution of the free neutron to proton ratio, the neutron and the proton transverse flows as a function of rapidity. The momentum dependence of nuclear symmetry potential affects the neutron-proton differential transverse flow more evidently than the difference of neutron and proton transverse flows as well as the difference of proton and neutron elliptic flows. It is thus better to probe the symmetry energy by using the difference of neutron and proton flows since the momentum dependence of nuclear symmetry potential is still an open question. And it is better to probe the momentum dependence of nuclear symmetry potential by using the neutron-proton differential transverse flow the rapidity distribution of the free neutron to proton ratio.     

Baryon distributions in ultrarelativistic nucleus-nucleus collisions

We have measured distributions in transverse momentum and rapidity of protons from interactions of 14.6 GeV/nucleon²⁸Si projectiles with targets of Al and Pb. The transverse momentum spectra exhibit a thermal shape with a rapidity dependent temperature parameter. For very central or violent collisions the proton rapidity distributions exhibit the large rapidity shifts and (for Si+Al) a peak at midrapidity as required for full stopping.     

Features of CC interactions at a momentum of 4.2 GeV/c per nucleon for various degrees of nuclear-collision centrality

The multiplicity, rapidity, and transverse-momentum distributions of secondaries (negative pions and protons) from CC interactions characterized by various numbers of participant protons are presented. It is shown that, in contrast to the mean transverse momenta of protons, the mean transverse momenta of pions depend only slightly on the degree of collision centrality. The shape of the rapidity distributions of negative pions is also weakly dependent on the degree of collision centrality. With decreasing impact parameter, the product protons are found to concentrate in the central rapidity region. The data in question are analyzed within the modified version of the FRITIOF model. It is shown that, as soon as elastic nucleon rescatterings are taken into account, the model describes satisfactorily the experimental features of negative pions and fast protons. The spectra of slow protons are described only qualitatively because of limitations of the evaporation model used here to treat the deexcitation of residual nuclei.     

Further development of a model for the production of strange particles in nucleus-nucleus collisions

A previously proposed model for the production of neutral strange particles in nucleus-nucleus collisions, based on the Additive Quark Model and nuclear cascading, is further developed. The model predictions on neutral strange particle multiplicities, transverse momentum and rapidity distributions are compared with the existing oxygen- and sulphur-nucleus data at 200 GeV per nucleon. The predictions for central PbPb collisions are presented and discussed in some detail.     

J/psi production versus transverse momentum and rapidity in p+p collisions at square root s=200 GeV

J/psi production in p+p collisions at square root s=200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over a rapidity range of -2.2相似文献   

Two-particle correlations in 360 GeV/cp p interactions

Two particle correlations of hadrons produced in 360 GeV/cpp interactions are investigated in the transverse plane and in rapidity. The data were obtained at the European hybrid spectrometer equipped with a rapid cycling bubble chamber. The observed transverse and rapidity correlations are compared with the one string LUND-and a two string dual parton-model. These models predict in general stronger correlations in the transverse plane and much weaker correlations in rapidity than found in the data. The LUND-FRITIOF-and multichain dual parton models provide a better reproduction of the data, although the agreement is not yet satisfactory. Only the UA5 cluster model GENCL shows agreement with the data.     

Unintegrated gluon distributions and Higgs boson productionin proton-proton collisions

Inclusive cross sections for Higgs boson production in proton-proton collisions are calculated in the formalism of unintegrated gluon distributions (UGDFs). Different UGDFs from the literature are used. Although they were constructed in order to describe the HERA deep-inelastic scattering F₂ data, they lead to surprisingly different results for Higgs boson production. We present both the two-dimensional invariant cross section as a function of Higgs boson rapidity and transverse momentum, as well as the corresponding projections on rapidity or transverse momentum. We quantify the differences between different UGDs by applying different cuts on interrelations between the transverse momentum of the Higgs and the transverse momenta of both fusing gluons. We focus on the large rapidity region. The interplay of the gluon-gluon fusion and weak-boson fusion in rapidity and transverse momentum is discussed. We find that above p_t ∼ 50–100 GeV the weak-gauge boson fusion dominates over gluon-gluon fusion. PACS. 12.38.Bx,12.38.Cy,13.85.Qk,14.70.Hp,14.80.Bn     

Intermittency model for rapidity particle density fluctuations

The one-dimensional model of intermittency is applied to particle density fluctuations in rapidity. Intermittency may explain the “anomalous” events with large density of particles in small rapidity windows and the, approximately energy-independent, linear relation between the average maximum rapidity density and the multiplicity. The connection of “host-spots” in rapidity with large transverse energy jets and the formation of the quark-gluon plasma is briefly discussed.     

Glasma flux tubes and the near side ridge phenomenon at RHIC

We investigate the consequences of long range rapidity correlations in the Glasma. Particles produced locally in the transverse plane are correlated by approximately boost invariant flux tubes of longitudinal color electric and magnetic fields that are formed when two sheets of Colored Glass Condensate pass through one another, each acquiring a modified color charge density in the collision. We argue that such long range rapidity correlations persist during the evolution of the Quark–Gluon Plasma formed later in the collision. When combined with transverse flow, these correlations reproduce many of the features of the recently observed ridge events in heavy ion collisions at RHIC.     

Inclusive photoproduction of neutral pions in the photon hemisphere at HERA

The inclusive cross section for the photoproduction of neutral pions has been measured as a function of the transverse momentum, rapidity, and Feynman x of the mesons at an average photon–proton centre-of-mass energy of 208 GeV and for photon virtualities below GeV. The measurement extends the range covered by previous charged particle measurements at HERA by two units of rapidity in the photon direction down to a value of in the centre-of-mass frame. The transverse momentum distribution is well described over the whole measured range by a power law ansatz, while an exponential fit falls below the data at transverse momentum values above 1.5 GeV/c. Good agreement with the predictions of the Monte Carlo models PYTHIA and PHOJET is found. In the context of the PYTHIA model the data are inconsistent with large intrinsic transverse momentum values in the photon. Received: 14 June 2000 / Published online: 27 November 2000     

Strange particle production in relativistic nucleus-nucleus collisions at RHIC and LHC energy regions

PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au＋Au collisions and in Pb＋Pb collisions with the √SNN = 200 GeV at the RHIC and 2.76 TeV at the LHC, respectively. The experimental results at different centralities, using data from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism for strange quark suppression, that are implemented in the PACIAE model.